The overall objectives of this proposal are to determine (1) the functional role of a number of nucleotide degrading enzymes in cell metabolism and (2) the molecular mechanisms involved in regulating the level of these enzyme activities, which in turn regulate the levels of nucleotide intermediates. The enzymes that we will study include: DR5P aldolase, purine nucleoside phosphorylase, phosphoribomutase, dCMP deaminase, 5' nucleotidase, and deoxyuridine phosphorylase. Our approach to the problem is the use of a combination of biochemical and genetic techniques. Biochemical approaches include purification of the enzymes from rat liver, preparation of antibodies made to the purified enzymes, and use of these antibodies as probes to study the regulation of the enzymes in cell cultures. Genetic approaches include isolation of mutant cell lines in Novikoff hepatoma cells and CHO cells that are deficient in one of the above enzymes or that overproduce one of the above enzymes. Mutants will be examined to determine the effect of the mutation on growth patterns, cell cycle transverse and regulation of nucleotide levels. The mutant cell lines will be used in cellular hybridization experiments to obtain information on the regulation of nucleotide degrading enzymes and to assign the structural genes coding for these enzymes to a particular rat chromosome. The information obtained from the proposed work should help us to understand the role that these nucleotide degrading enzymes play in mammalian cellular growth and metabolism.